如何查看 iOS 版本？

I want to check if the iOS version of the device is greater than 3.1.3 I tried things like:

[[UIDevice currentDevice].systemVersion floatValue]

but it does not work, I just want a:

if (version > 3.1.3) { }

How can I achieve this?

转载于:https://stackoverflow.com/questions/3339722/how-to-check-ios-version

The quick answer …

As of Swift 2.0, you can use #available in an if or guard to protect code that should only be run on certain systems.

if #available(iOS 9, *) {}

In Objective-C, you need to check the system version and perform a comparison.

[[NSProcessInfo processInfo] operatingSystemVersion] in iOS 8 and above.

As of Xcode 9:

if (@available(iOS 9, *)) {}

The full answer …

In Objective-C, and Swift in rare cases, it's better to avoid relying on the operating system version as an indication of device or OS capabilities. There is usually a more reliable method of checking whether a particular feature or class is available.

Checking for the presence of APIs:

For example, you can check if UIPopoverController is available on the current device using NSClassFromString:

if (NSClassFromString(@"UIPopoverController")) {
    // Do something
}

For weakly linked classes, it is safe to message the class, directly. Notably, this works for frameworks that aren't explicitly linked as "Required". For missing classes, the expression evaluates to nil, failing the condition:

if ([LAContext class]) {
    // Do something
}

Some classes, like CLLocationManager and UIDevice, provide methods to check device capabilities:

if ([CLLocationManager headingAvailable]) {
    // Do something
}

Checking for the presence of symbols:

Very occasionally, you must check for the presence of a constant. This came up in iOS 8 with the introduction of UIApplicationOpenSettingsURLString, used to load Settings app via -openURL:. The value didn't exist prior to iOS 8. Passing nil to this API will crash, so you must take care to verify the existence of the constant first:

if (&UIApplicationOpenSettingsURLString != NULL) {
    [[UIApplication sharedApplication] openURL:[NSURL URLWithString:UIApplicationOpenSettingsURLString]];
}

Comparing against the operating system version:

Let's assume you're faced with the relatively rare need to check the operating system version. For projects targeting iOS 8 and above, NSProcessInfo includes a method for performing version comparisons with less chance of error:

- (BOOL)isOperatingSystemAtLeastVersion:(NSOperatingSystemVersion)version

Projects targeting older systems can use systemVersion on UIDevice. Apple uses it in their GLSprite sample code.

// A system version of 3.1 or greater is required to use CADisplayLink. The NSTimer
// class is used as fallback when it isn't available.
NSString *reqSysVer = @"3.1";
NSString *currSysVer = [[UIDevice currentDevice] systemVersion];
if ([currSysVer compare:reqSysVer options:NSNumericSearch] != NSOrderedAscending) {
    displayLinkSupported = TRUE;
}

If for whatever reason you decide that systemVersion is what you want, make sure to treat it as an string or you risk truncating the patch revision number (eg. 3.1.2 -> 3.1).

Try:

NSComparisonResult order = [[UIDevice currentDevice].systemVersion compare: @"3.1.3" options: NSNumericSearch];
if (order == NSOrderedSame || order == NSOrderedDescending) {
    // OS version >= 3.1.3
} else {
    // OS version < 3.1.3
}

I recommend:

if ([[[UIDevice currentDevice] systemVersion] floatValue] > 3.13) {
    ; // ...
}

credit: How to target a specific iPhone version?

/*
 *  System Versioning Preprocessor Macros
 */ 

#define SYSTEM_VERSION_EQUAL_TO(v)                  ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] == NSOrderedSame)
#define SYSTEM_VERSION_GREATER_THAN(v)              ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] == NSOrderedDescending)
#define SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(v)  ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] != NSOrderedAscending)
#define SYSTEM_VERSION_LESS_THAN(v)                 ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] == NSOrderedAscending)
#define SYSTEM_VERSION_LESS_THAN_OR_EQUAL_TO(v)     ([[[UIDevice currentDevice] systemVersion] compare:v options:NSNumericSearch] != NSOrderedDescending)

/*
 *  Usage
 */ 

if (SYSTEM_VERSION_LESS_THAN(@"4.0")) {
    ...
}

if (SYSTEM_VERSION_GREATER_THAN_OR_EQUAL_TO(@"3.1.1")) {
    ...
}

As suggested by the official Apple docs: you can use the NSFoundationVersionNumber, from the NSObjCRuntime.h header file.

if (floor(NSFoundationVersionNumber) > NSFoundationVersionNumber_iOS_6_1) {
    // here you go with iOS 7
}

This is used to check for compatible SDK version in Xcode, this is if you have a large team with different versions of Xcode or multiple projects supporting different SDKs that share the same code:

#if __IPHONE_OS_VERSION_MAX_ALLOWED >= 80000
  //programming in iOS 8+ SDK here
#else
  //programming in lower than iOS 8 here   
#endif

What you really want is to check the iOS version on the device. You can do that with this:

if ([[[UIDevice currentDevice] systemVersion] floatValue] < 8.0) {
  //older than iOS 8 code here
} else {
  //iOS 8 specific code here
}

Swift version:

if let version = Float(UIDevice.current.systemVersion), version < 9.3 {
    //add lower than 9.3 code here
} else {
    //add 9.3 and above code here
}

Current versions of swift should be using this:

if #available(iOS 12, *) {
    //iOS 12 specific code here
} else {
    //older than iOS 12 code here
}

Preferred Approach

In Swift 2.0 Apple added availability checking using a far more convenient syntax (Read more here). Now you can check the OS version with a cleaner syntax:

if #available(iOS 9, *) {
    // Then we are on iOS 9
} else {
    // iOS 8 or earlier
}

This is the preferred over checking respondsToSelector etc (What's New In Swift). Now the compiler will always warn you if you aren't guarding your code properly.

Pre Swift 2.0

New in iOS 8 is NSProcessInfo allowing for better semantic versioning checks.

Deploying on iOS 8 and greater

For minimum deployment targets of iOS 8.0 or above, use NSProcessInfo operatingSystemVersion or isOperatingSystemAtLeastVersion.

This would yield the following:

let minimumVersion = NSOperatingSystemVersion(majorVersion: 8, minorVersion: 1, patchVersion: 2)
if NSProcessInfo().isOperatingSystemAtLeastVersion(minimumVersion) {
    //current version is >= (8.1.2)
} else {
    //current version is < (8.1.2)
}

Deploying on iOS 7

For minimum deployment targets of iOS 7.1 or below, use compare with NSStringCompareOptions.NumericSearch on UIDevice systemVersion.

This would yield:

let minimumVersionString = "3.1.3"
let versionComparison = UIDevice.currentDevice().systemVersion.compare(minimumVersionString, options: .NumericSearch)
switch versionComparison {
    case .OrderedSame, .OrderedDescending:
        //current version is >= (3.1.3)
        break
    case .OrderedAscending:
        //current version is < (3.1.3)
        fallthrough
    default:
        break;
}